Prior to the present invention, various methods were employed to synthesize bisphenols, such as bisphenol-A, by effecting reaction between a ketone and a phenol. One procedure, for example, involved the use of large amounts of inorganic acid catalysts, such as sulfuric acid or hydrochloric acid. Experience has shown, however, that the use of inorganic acids requires a means to neutralize such acids at the end of the reaction due to the corrosive action of the strong acids. In addition, distillation of the resulting bisphenol is often required because of the many by-products formed during the reaction under high acid conditions.
An improved procedure was developed by using a solid resin cation-exchange catalyst to effect the condensation between the phenol and the ketone. However, the disadvantage of the ion-exchange catalyst is the low acid concentration it provides resulting in the need for a rate accelerator such as a mercaptan. One procedure is shown by Apel et al, U.S. Pat. No. 3,153,001, which incorporates the mercaptan by partial esterification of the ion-exchange catalyst in the form of a sulfonated insoluble polystyrene resin. Another procedure involves the partial neutralization of such sulfonic acid moiety with an alkyl mercapto amine, as shown by McNutt et al, U.S. Pat. No. 3,394,089. A further procedure is shown by Wagner et al, U.S. Pat. No. 3,172,916, based on the partial reduction of the sulfonic acid to afford thiophenol functional groups. It has been found, however, that Wagner et al does not afford a particularly active type of promoter for synthesizing bisphenols, such as bisphenol-A. The methods of Apel et al and McNutt et al are also unsatisfactory after extended use under continuous reaction conditions, since the ion-exchange resins used in these methods readily lose mercaptan when attempts are made to regenerate them.
In copending application Ser. No. 103,095, filed Dec. 13, 1979 there is taught that N-organoaminodisulfide of the formula, ##STR1## where X is a halogen radical or a counter ion, such as sulfate, Y is selected from hydrogen, carboxy and nitrile and R is a C.sub.(1-13) divalent organic radical selected from aliphatic and aromatic radicals, can be used to incorporate covalently bonded organo mercaptan groups into the backbone of the sulfonated aromatic organic polymer. Although improved results were obtained by using such ion-exchange resin to form bisphenols from phenol and acetone as compared to the aforementioned resins of the prior art, it was found that the use of such catalyst to form bisphenol from acetone and phenol under continuous reaction conditions resulted in a gradual reduction in the percent conversion of bisphenol during the course of the reaction.
The present invention is based on the discovery that N-alkylaminoorgano disulfide of the formula, ##STR2## can be used to produce sulfonated aromatic organic polymer containing N-alkylaminoorgano mercaptan groups attached to backbone sulfonyl radicals by covalent nitrogen-sulfur linkages, exhibiting substantially enhanced stability under continuous reaction conditions during the production of bisphenol from a ketone and phenol without a significant reduction in rate of bisphenol formation as compared to the aforementioned ion-exchange resin provided by the copending application Ser. No. 103,095 as described above, where R.sup.1 is a C.sub.(1-8) monovalent alkyl radical and R, X and Y are as previously defined.
It has been found that after chemical attachment of the N-alkylaminoorgano disulfide of formula (1) to the polymer backbone as defined below, it can be reduced with a triorganophosphine, whereby the disulfide is converted to a mercaptan after acidification.